Progressive power multifocal lens
AssigneeHoya Corporation
InventorAkira Kitani
Life of this patent
Estimating the term…
Abstract
A progressive power multifocal lens designed by attaching importance to an intermediate vision and a near vision in such a manner as to ensure broad intermediate vision viewing portion and near vision viewing portion and to have a well-balanced viewing zone among the distance, near and middle portions, whereby a resultant image of an object is little varied or fluctuated, especially, in lateral directions.
Claims5
A progressive power multifocal lens having a far vision power measuring position, a near vision power measuring position and an eye-point position, through which a visual line runs when being in a front viewing condition, which are preliminarily located,
- wherein an additional surface refractive power between surface refractive powers respectively obtained at the near vision power measuring position and at the far vision power measuring position is equal to an addition,
- wherein the progressive power multifocal lens satisfies the following conditions:
- (a) the additional surface refractive power at the eye-point position is not less than 30% and not more than 50% of the addition;
- (b) the lens has no axis of symmetry that bisects an entire surface thereof, and the lens for the right eye has a refracting surface which is different from a refracting surface of the lens for the left eye;
- (c) the eye-point position is located closer to a nose than the far vision power measuring position:
- and the near vision power measuring position is further situated closer to the nose thereof than the eye-point position in such a manner that both cases of the lens for the right eye and the lens for the left eye are adapted to a convergence action of the eyes when viewing a near place;
- (d) the far vision power measuring position is upwardly deviated from the eye-point position by a distance of 10 to 17 mm;
- and the near vision power measuring position is downwardly deviated from the eye- point position by a distance of 14 to 21 mm;
- and
- (e) assuming that the far vision power measuring position is used as a center and that a direction, in which a horizontal half-line extends rightwardly from the far vision power measuring position, is determined as a reference direction whose azimuth angle is 0, a nearly sectorial domain corresponding to azimuth angles of 30 to 150 degrees is used as a far viewing distinct vision zone in which astigmatism is not more than 0.5 diopters irrespective of the value of the addition.
Dependencies are inferred from the claim text.